Viewing apparatus

ABSTRACT

Viewing apparatus for providing a viewer with an apparent 3-D image includes a diffusing holographic optical element screen, horizontal strip lamps for illuminating the screen from a plurality of different positions and a liquid crystal display for effecting spatial modulation of the light from the respective positions so as to illuminate respective images on the screen. The arrangement is such as to provide a plurality of viewing zones whereby each image can be seen only from a corresponding one of the zones.

FIELD OF THE INVENTION

This invention relates to viewing apparatus particularly, but notexclusively, for providing a viewer with an apparent 3-D image.

BACKGROUND OF THE INVENTION

Stereoscopic apparatus exists in which a pair of nearly identical imagesare viewed through a binocular optical system to provide the viewer witha perception of a single 3-D image. A disadvantage of such apparatus isthe necessity of having to provide such an optical system, usually inthe form of a pair of goggles, for use by the viewer.

In effect, such a system provides for viewing a plurality of sets ofjuxtaposed information and it would be a considerable advantage if thiscould be achieved without the necessity for the viewer to have to beprovided with a pair of goggles.

SUMMARY OF THE INVENTION

According to the present invention, there is provided viewing apparatuscomprising a holographic recording (15) of a diffusely illuminated zone(5,9) and means (17, 19) for illuminating the holographic recording (15)from a plurality of different positions such that images (18,20) of thezone (5,9) are reconstructed forming viewing zones (18,20) characterisedin that there is provided adjacent the holographic recording (15) anon-projected masking means 14 for effecting spatial modulation of lightfrom the respective positions, the arrangement being such as to providea plurality of viewing zones (18,20) whereby the said spatial modulationcan be seen from a corresponding one of the zones (18,20).

Following is a description, by way of example only and with reference tothe accompanying drawings, of one method of carrying the invention intoeffect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of one method of recording adiffusing holographic optical element (HOE) for apparatus in accordancewith the present invention.

FIG. 2 is a diagrammatic perspective view of another method of recordinga diffusing HOE for apparatus in accordance with the present invention.

FIG. 3 is a diagrammatic perspective view of an embodiment of apparatusin accordance with the present invention.

FIG. 4 is a diagrammatic representation of another embodiment ofapparatus in accordance with the present invention.

FIG. 5 is an enlarged view of a portion of the apparatus shown in FIG.3.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawings, there is shown apparatus forproviding a master hologram from which many HOEs can be formed. A beamfrom a laser 1 is split by a beam splitter 3 into two beams. One of thebeams, a reference beam is expanded by a beam expander 2 and reflectedat a concave mirror 7 as a parallel (collimated) beam 8 which impingeson a holographic plate 6. The other of the beams is expanded by a beamexpander 4 and is directed towards a diffuser 5 which scatters the lighttowards the holographic plate 6 where it interferes with the referencebeam and a hologram of the diffuser is recorded.

In the arrangement shown in FIG. 2 of the drawings the laser 1, the beamsplitter 3 and the beam expanders 2 and 4 are provided as in theapparatus shown in FIG. 1 but the collinated beam 8 now becomes arestructuring beam. The master 6 is reversed before being replaced inthe beam, this means that the beam is the conjugate of the originalreference beam and a real image 9 of the diffuser is formed. A second(unexposed) holographic plate 12 is placed between the plate 6 and animage 9. The plate 12 is provided with a reference beam 11 spreadingfrom a beam expander 10 placed close to the plate 12. The light from thereference beam 11 and the light forming the image of the diffuserinterfere and the resulting pattern is recorded by the plate 12 and theHOE is thereby formed.

The plate 12 may be provided as a component in the screen or as a toolfor use in the manufacture of additional similar HOEs.

As an alternative to manufacturing such HOEs it is possible to replicatethem optically by contact copying. In either process the holographicmaterial should exhibit a good diffraction efficiency and a good signalto noise ratio. Examples of material embodying such characteristics arephotopolymer and dichromated gelatine (D.C.G.) Alternativelty, the HOEmay be reproduced as a surface relief pattern which might be embossed ormoulded in clear plastic.

Referring now to FIG. 3 of the drawings, there is shown a diagrammaticperspective view of an embodiment of viewing apparatus in accordancewith the invention. A HOE 15 is made using a narrow vertical stripdiffuser. The HOE 15 is located between a liquid crystal display (LCD)14 and a louvred screen 16 and the HOE 15 is illuminated from the sidethereof adjacent the screen 16 by a beam 13 from a horizontal strip lamp17. A second horizontal strip lamp 19 is provided adjacent the lamp 17.

The HOE 15 is made using a narrow vertical strip diffuser. A real imageof this diffuser is formed and spread sideways at 18 when the HOE 15 isilluminated by the strip lamp 17. When the strip lamp 19 is activated, areal image is formed at 20.

The louvred screen 16 is adapted to receive light at a predeterminedangle of incidence, for example 55°, but is opaque when viewed at otherangles. It prevents a viewer from looking through the screen whilepermitting light from the lamps 17, 19 to pass through it and strike theHOE 15 at a correct angle. It thereby improves contrast.

When the lamp 17 is operative, light from the lamp passes through thelouvred screen 16, is diffracted by the HOE 15, passes through the LCD14 and then forms a spread real image of the diffuser at 18.

If the screen is viewed from a position around the image 18 or, morespecifically, if the eye is positioned such that all straight linesdrawn through the observer's eye and points on the screen also passthrough the real image 18, the whole screen will be seen to beilluminated and whatever image there is on the LCD 14 will be visible.If the screen is viewed from around the zone 20 the screen will be darkand the image invisible. Conversely, if the lamp 19 is operative and thelamp 17 is inoperative the LCD image will be visible from the zone 20but not from the zone 18.

If there are two alternating images on the LCD 14 and the two lamps 17and 19 are operational alternately in synchronism with the alternatingimages, one image will be visible from zone 20 and the other from zone18. If the two images are a stereo pair and if the viewer is positionedsuch that one eye is in zone 18 and the other eye is in zone 10 theimage will be seen in stereoscopic 3-D.

It will be appreciated that the number of viewing zones need not belimited to two--for example the number of views may be increased,alternatively the views could be repeated to each side allowing morethan one person at a time to see a stereo pair.

It will be appreciated that the diffusers need not be narrow strips butmay also be wide.

It will be appreciated that the diffusers do not need to be parallel tothe HOE but may be inclined to it.

It will be appreciated that the lamps may have any spectralcharacteristics, for example white or monochromatic.

It will be appreciated that the illumination may be direct, or make useof diffraction gratings, lenses, prisms, mirrors or other opticaldevices to direct the light towards the HOE.

It will be appreciated that additional optics may be incorporated toeffect dispersion compensation.

It will be appreciated that the light sources need not be located belowthe screen but may be in a variety of other positions, according to howthe HOE is made and the effect of additional optical elementsincorporated in the apparatus.

It will be appreciated that the strip lamps may be replaced by groups oflamps. For example each strip lamp may be replaced with a group of lampscomprising one of each primary colour.

It will be appreciated that the strip lamps may be replaced withindividual or grouped smaller sources for example point LEDs.

It will be appreciated that the HOE may be made using a plurality ofdiffusers and that this will give rise to there being a plurality ofsimilar viewing zones.

It will also be appreciated that the screen may be used for showingseveral sets of information and not necessarily in 3-D. For example, thetwo images which are viewed at the zones 18,20 could be a standardstereo pair either as a photographic 'still or as a moving film. Inanother example, two sets of information can be shown at the respectiveviewing zones 18,20 and this would double the effective screen areasince a viewer would only have to move his or her head to switch fromone image to another.

Nevertheless, there are many advantgages for the 3-D application, forexample in the field of computer aided design and stereo presentation ofcomputer VDU outputs and arcade and personal computer games. It shouldalso be possible to combine two discreet sets of information with astereo image.

Referring now to FIGS. 4 and 5 of the drawings, there is shown apparatuscomprising a holographic screen 21 and a plurality of lamps 22 spacedone from another each for illuminating the screen 21. The screen 21 isof similar construction to the combination of the components 14, 15 and16 in the previous example which, when illuminated by any one of thelamps 22 projects from the screen 20 a real image of a verticaldiffuser. The beam of light from each of the lamps 22 is spatiallymodulated in such a way as to cast an image on the screen 21.

The lamps 22 are arranged to switch on and off sequentially, the effectbeing that the real image of the diffuser is seen to move horizontally.The speed of operation of the lamps 22 is sufficient for persistence ofvision. If the images that are produced correspond to different anglesof view of a 3-D object, whether real or artificially generated, and itis arranged that each eye of the viewer sees different views of theobject corresponding to the correct stereo pair, the object will beviewed in 3-D.

The number of views may be three or more. If there are many such views(say approximately 100) then there will be sufficient viewing angle andthe slits can be narrow enough (say 2 mm wide) for there to be thesensation of continuous paralax giving the possibility of looking aroundthe image.

We claim:
 1. Viewing apparatus comprising a holographic recording of adiffusely illuminated zone and means for illuminating the holographicrecording from a plurality of different positions such that images ofthe zone are reconstructed forming viewing zones characterised in thatthere is provided adjacent the holographic recording a modulating screenfor effecting spatial modulation of light from the respective positions,the arrangement being such as to provide a plurality of viewing zoneswhereby the said spatial modulation can be seen from a corresponding oneof the zones.
 2. Apparatus as claimed in claim 1 characterised in thatlight emanates from the different positions sequentially so as toilluminate sequentially respective images on said screen.
 3. Apparatusas claimed in claim 2 characterised in that images are arranged instereo pairs and the sequential illumination is of a speed such as toprovide persistence of vision.
 4. Apparatus as claimed in claim 3characterised in that said modulating screen having means responsive toelectrical signals for controlling transmission of light therethrough.